A ubiquitous mobile genetic element disarms a bacterial antagonist of the gut microbiota

Abstract

AbstractDNA transfer is ubiquitous in the gut microbiota, especially among species of Bacteroidales.In silicoanalyses have revealed hundreds of mobile genetic elements shared between these species, yet little is known about the phenotypes they encode, their effects on fitness, or pleiotropic consequences for the recipient’s genome. Here, we show that acquisition of a ubiquitous integrative and conjugative element encoding an antagonistic system shuts down the native contact-dependent antagonistic system ofBacteroides fragilis. Despite inactivating the native antagonism system, mobile element acquisition increases fitness of theB. fragilistransconjugant over its progenitor by arming it with a new weapon. This DNA transfer causes the strain to change allegiances so that it no longer targets ecosystem members containing the same element yet is armed for communal defense.